Population Dynamics of a Reintroduced Population of Captive-Raised Gibbons (Hylobates lar) on Phuket, Thailand

Abstract

Confiscated and donated white-handed gibbons ( Hylobates lar) originating from the local wildlife trade have been rescued by the Gibbon Rehabilitation Project (GRP) and rehabilitated on Phuket since 1992. Here we present some results of this long-term gibbon reintroduction project. Following unsuccessful early release attempts beginning in 1993, GRP has experi- mented with reintroduction methods and developed a protocol that has succeeded in re-establishing a small independent breeding population in a 22-km 2 forest fragment on Phuket. Eight breeding families of gibbons were released into the Khao Phra Thaew non-hunting area between October 2002 and November 2012 using a soft-release reintroduction method in which the gibbons were provisioned with fresh food in the trees for at least one year, or as long as they needed it. The adult pair in the first gibbon family that was reintroduced there has remained together for 10 years post-release, they have maintained the original pair-bond and raised three wild-born offspring. The reintroduced population has seen eleven infants born in the wild, including a second- generation gibbon born to the first wild-born female. Female interbirth intervals and ages at first reproduction in the reintroduced population are comparable with those in wild populations. Of the seven adult females originally released, two remain with their original mates and two remain in the wild paired with different mates. By the end of 2012, three of the six wild groups were not nuclear families, indicating a flexibility of group composition seen in well-studied wild populations.